Tumor cells can be lysed in vivo and in vitro by cytotoxic effector cells, cytotoxic biological molecules, and drugs. Under proper conditions, tumor cell resistance to any one of these agents can be induced. The possible relationship between pleiotropic drug resistance (PDR) and tumor cell resistance to cell-mediated cytotoxicity (CMC) reactions or cytotoxins has not yet been investigated. This proposal is based on the new finding that selection of tumor cell variants in vitro with ceratin cytokines induces the coordinant expression of PDR and resistance to certain types of CMC reactions. The hypothesis to be tested is that tumor cells can acquire the ability to resist lysis by diverse cytotoxic agents though some common underlying mechanisms. To determine if this is a widespread phenomenon, various types of cell lines will be selected by growth in natural killer cytotoxic factors (NKCF), recombinant tumor necrosis factor (rTNF), recombinant interferon (rIFN), rTNF combined with rIFN , or by various cytotoxic drugs. The resulting variants will be characterized with respect to sensitivity to lysis by cytokines, NK CMC, antibody-dependent CMC, lectin-dependent CMC (LDCC) macrophage CMC, and various cytotoxic drugs. Some of the variants will be tested for undergoing differentiation and maturation in response to cytokine selection. Experiments will be carried out to determine what defects in the variants are responsible for resistance to lysis. The role of TNF receptors in cell lysis by rTNF,and NK cells will be examined. The mechanism of drug resistance will be examined by testing for reversal of resistance with calcium channel blockers and calmodulin inhibitors and measuring drug uptake and efflux. Variants will be analyzed for overexpression of PDR-associated membrane proteins not found in the parental line. Karyotype analysis will be performed on all variants. Gene transfer studies will be carried out to determine if the phenotypic expression of pleiotropic resistance is governed by closely linked genes or completely different mutations. Transformants will be characterized with respect to sensitivity to the various cytotoxic agents, expression of TNF receptors, and expression of PDR-associated membrane proteins. Thus, it should be possible to correlate genetic alterations with gene products underlying resistance to the cytotoxic agents. These studies should help to elucidate the mechanism of tumor cell lysis by cytotoxins and cytotoxic effector cell. They may also provide a basis for the cloning of genes involved in tumor cell resistance to lysis.